Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A22: Surfaces, Interfaces and Polymeric Thin Films |
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Sponsoring Units: DPOLY Chair: Joshua Sangoro, University of Tennessee-Knoxville Room: 407 |
Monday, March 3, 2014 8:00AM - 8:12AM |
A22.00001: The effect of block-copolymer structures on the polymeric liquid-liquid interface: Molecular Dynamic Study Jiho Ryu, Won Bo Lee, Bumjoon Kim The change of free energy caused by different morphology of surfactants (block- and grafted-copolymers) in the biphasic system, is investigated by molecular dynamic simulations. We studied two different structures of surfactants. Type 1 is a diblock-copolymer surfactant composed with 60 monomers(30 A beads and 30 B beads). Type 2 is a grafted-copolymer surfactant of which two side chains composed of, respectively, 15 B monomers, are attached to main back bone chain composed of 30 A monomers. All simulations were performed in the NVT ensemble at 373K. Free energy are computed by thermodynamic integration from the coupled state to the uncoupled state where the surfactant does not interact with the biphasic system. In addition, we discuss various effects such as stiffness of polymers. [Preview Abstract] |
Monday, March 3, 2014 8:12AM - 8:24AM |
A22.00002: Relaxation and Intermediate Asymptotics of a Surface Perturbation in a Viscous Film Oliver B\"aumchen, Michael Benzaquen, Thomas Salez, Joshua D. McGraw, Matilda Backholm, Paul Fowler, Elie Rapha\"el, Kari Dalnoki-Veress The surface of a thin liquid film with nonconstant curvature flattens as a result of capillary forces. While this leveling process is driven by local curvature gradients, the global boundary conditions greatly influence the dynamics. Here, we study the evolution of rectangular trenches in a polystyrene nanofilm. We report on full agreement between theory and experiments for the capillary-driven flow and resulting time dependent height profiles, a crossover in the power-law dependence of the viscous energy dissipation as a function of time as the trench evolution transitions from two noninteracting to interacting steps, and the convergence of the profiles to a universal self-similar attractor that is given by the Green's function of the linear operator describing the dimensionless linearized thin film equation. [Preview Abstract] |
Monday, March 3, 2014 8:24AM - 8:36AM |
A22.00003: Filling up of a cylindrical hole in a viscous film Matilda Backholm, Michael Benzaquen, Thomas Salez, Elie Raphael, Kari Dalnoki-Veress A small cylindrical hole is a naturally occurring surface perturbation in viscous films. The flow dynamics of the hole is relevant for industrial applications, but more generally also important for the understanding of relaxation processes in thin films. Here, the capillary levelling of cylindrical holes in viscous polystyrene films was studied using atomic force microscopy and analytical scaling arguments. The relaxation of holes of various sizes was shown to consist of two different time regimes: an early regime where opposing sides of the hole do not interact, and a late regime where the hole is filling up. All theoretically derived scaling laws as well as the long-term solution of the intermediate asymptotic regime were shown to be in excellent agreement with experiments. In short, the system presented here provides an ideal sample geometry with which to probe flow on the nano-scale. [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 8:48AM |
A22.00004: The Rayleigh-Plateau Instability on a Fiber Revisited - Influence of the Hydrodynamic Boundary Condition Sabrina Haefner, Oliver Baeumchen, Michael Benzaquen, Thomas Salez, Robert Peters, Joshua D. McGraw, Elie Raphael, Karin Jacobs, Kari Dalnoki-Veress The Rayleigh-Plateau Instability (RPI) of a liquid column underlies a variety of hydrodynamic phenomena that can be observed in everyday life. In the classical case of a free liquid column, linear perturbation theory predicts characteristic rise-times and wavelengths. However, the description of a liquid layer on a fiber requires the consideration of the solid/liquid interface in addition to the free interface. In this study, we revisit the RPI of a viscous liquid layer on a solid fiber by varying the hydrodynamic boundary condition at the fiber/liquid interface. The rise of the amplitudes of the surface undulations is precisely tracked and the growth rate of the instability is determined for the different slip boundary conditions and compared to the theoretical models. [Preview Abstract] |
Monday, March 3, 2014 8:48AM - 9:00AM |
A22.00005: Influence of Slip on the Rayleigh-Plateau Rim Instability in Dewetting Viscous Films Ralf Blossey, Oliver Baeumchen, Ludovic Marquant, Sabrina Haefner, Andreas M\"unch, Dirk Peschka, Barbara Wagner, Karin Jacobs A viscous film that retracts from a solid substrate develops a characteristic fluid rim at its receding edge due to mass conservation. In the course of this dewetting process the rim becomes unstable via an instability of Rayleigh-Plateau type. An important difference exists between this classic instability of a liquid column and the rim instability in the liquid film as the growth of the rim is continuously fueled by the receding film. We explain how the development and macroscopic morphology of the rim instability are controlled by the slip of the film on the substrate. Numerical calculations of a single thin-film model capture quantitatively the characteristics of the evolution of the rim observed in our experiments. [Preview Abstract] |
Monday, March 3, 2014 9:00AM - 9:12AM |
A22.00006: Controlling Marangoni induced instabilities in spin-cast polymer films: How to prepare uniform films Paul Fowler, C\'{e}line Ruscher, James Forrest, Kari Dalnoki-Veress In both research and industrial settings spin coating is extensively used to prepare thin polymer films of reproducible thickness. Normally spin coating produces highly uniform films, however under certain conditions the spin coating process results in films with non-uniform surface morphologies. Although the spin coating process has been extensively studied, the origin of these morphologies is not fully understood and the formation of non-uniform spincast films remains a practical problem. Here we report on experiments indicating that the formation of surface instabilities during spin coating is dependent on temperature. Furthermore, we find that non-uniformities in the film thickness can be entirely avoided simply by changing the spin coating temperature. [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:24AM |
A22.00007: Time and temperature dependent wrinkling of stiff thin films on shape memory polymers Yu Wang, Kai Yu, Jerry Qi, Jianliang Xiao Shape memory polymers (SMPs) can remember two or more distinct shapes, and therefore can have a lot of potential applications. We here present combined experimental and theoretical studies on the wrinkling of stiff thin films on SMPs. Experimental results show well-defined, wavy profiles of the thin films. Time and temperature dependent wrinkle formation and evolution were observed. Finite element simulations accounting for the thermomechanical behavior of SMPs were used to study wrinkling of thin films on SMPs, which show good agreement with experiments. This study can have important implications in surface engineering, stretchable electronics and advanced manufacturing. [Preview Abstract] |
Monday, March 3, 2014 9:24AM - 9:36AM |
A22.00008: Frictional Response of Molecularly Thin Liquid Polymer Films Subject to Constant Shear Stress Charles Tschirhart, Sandra Troian Measurements of the frictional response of nanoscale viscous films are typically obtained using the surface force apparatus in which a fluid layer is confined between smooth solid substrates approaching at constant speed or force. The squeezing pressure causes lateral flow from which the shear viscosity can be deduced. Under these conditions however, molecularly thin films tend to solidify wholly or partially and estimates of the shear viscosity can exceed those in macroscale films by many orders of magnitude. This problem can be avoided altogether by examining the response of an initially flat, supported, free surface film subject to comparable values of surface shear stress by application of an external inert gas stream. This method was first conceived by Derjaguin in 1944; more recent studies by Mate et al. at IBM Almaden on complex polymeric systems have uncovered fluid layering and other interesting behaviors. The only drawback is that this alternative technique requires an accurate model for interface distortion. We report on ellipsometric measurements of ultrathin polymeric films in efforts to determine whether the usual interface equations for free surface films based purely on continuum models can be properly extended to nanoscale films. [Preview Abstract] |
Monday, March 3, 2014 9:36AM - 9:48AM |
A22.00009: Inducing surface morphologies in polymer films through exposure to non-solvents Chad Daley, Zin Tun, James Forrest Non-solvents are generally considered to have no lasting effect on polymer materials and are commonly employed in the production or processing of thin film polymer samples. Through a combination of atomic force microscopy and neutron reflectivity experiments we show that some non-solvents have the ability to drastically alter a film's surface morphology on the nanometer scale. An explanation for the structuring process is presented and reinforced through theoretical considerations of surface chains. These results suggest that caution should be exercised when making use of non-solvents wherever nanoscale surface properties are of importance. [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A22.00010: Single-Molecule Tracking of Polymer Surface Diffusion Michael Skaug, Joshua Mabry, Daniel Schwartz The mobility of polymers adsorbed on a solid surface is important in thin film formation, adhesion phenomena and biosensing applications, but it is still poorly understood. We used single-molecule fluorescence experiments to follow the motion of isolated polyethylene glycol chains adsorbed at a hydrophobic solid-aqueous interface. We found that molecules moved on the surface via a continuous time random walk mechanism, where periods of immobilization were punctuated by flights through the bulk liquid. The dependence of surface mobility on molecular weight suggested that surface-adsorbed polymers maintained effectively three-dimensional surface conformations. These results indicate that polymer surface diffusion, rather than occurring in the two dimensions of the interface, is dominated by a three-dimensional mechanism that leads to large surface displacements and significant bulk-surface coupling. [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A22.00011: Diffusion of polyelectrolyte chains within layer-by-layer films: effect of film stratification Victor Selin, Aliaksandr Zhuk, John F. Ankner, Svetlana Sukhishvili We compare the molecular weight dependence of the diffusion of polyelectrolyte chains within polyelectrolyte multilayer films with a different degree of internal layer intermixing. Linearly and ``exponentially'' grown films were prepared by the layer-by-layer (LbL) technique using poly(methacrylic acid) (PMAA) as a polyanion and quaternized poly-2-(dimethylamino)ethyl methacrylate (QPDMAEMA) as a polycation. Diffusion of polyelectrolyte chains in directions parallel and perpendicular to the film surface was measured using fluorescence recovery after photobleaching (FRAP) and neutron reflectometry (NR), respectively. We find that in solutions of 0.2-0.4~M~NaCl, lateral chain diffusion is enhanced in the exponential regime. More importantly, the scaling of the center-of-mass diffusion of polyelectrolyte chains with polymer molecular weight changed from a $D \sim M^{-1}$ dependence in the linear regime to a stronger dependence for the exponential regime, where polymer chains were stronger intermixed. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A22.00012: Nano-rheometry near the free-surface in polystyrene Kurt M. Schreiter, James A. Forrest Recent work has suggested enhanced mobility at the free-surface of glassy polymers. Traditional rheometers are incompatible with free surfaces so they cannot be used to confirm this. Lateral force spectroscopy has failed to observe deviations from bulk behaviour because the time scales required are too fast. We describe a technique for observing near surface dynamics in the free surface of soft matter systems that overcomes these limitations. Data collected from polystyrene films shows two simultaneous and separate relaxation behaviours. One of these is consistent with a bulk glassy material and the other indicates enhanced dynamics. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A22.00013: Hydrogen-bond Dynamics at The Interface Between Water and Oxidized Atactic Polystyrene Selemon Bekele, Mesfin Tsige Hydrogen bonding is very critical to a wide range of systems, from the existence of liquid water at room temperature to the structure of DNA (double helix) and many other biomolecules. The presence of an interface is expected to significantly change the structure and dynamics of the hydrogen bonded network as compared to the situation in the bulk. Understanding the strength and dynamics of hydrogen bonds at surfaces and interfaces has thus stimulated a large and growing body of experimental and theoretical work in recent years. Using all-atom molecular dynamics simulations we have studied the dynamics of hydrogen-bond (H-bond) between water and oxidized atactic polystyrene (aPS). The number of hydrogen bonds between water molecules and oxidized polystyrene is found to monotonically increase with oxygen concentration on the aPs surface. The life-time of this H-bond and the frequency of its formation have also been investigated as a function of oxygen concentration and the results will be presented. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A22.00014: Binding kinetics of lock-key colloids: surface diffusion enhancement of the rate of specific binding Laura Colon-Melendez, Daniel J. Beltran-Villegas, Greg van Anders, Jun Liu, Matthew Spellings, Stefano Sacanna, David J. Pine, Sharon C. Glotzer, Ronald G. Larson, Michael J. Solomon The kinetics of anisotropic particle assembly are expected to be slow due to specific directional interactions between the assembly building blocks. We investigate the lock-and-key colloidal system (Sacanna et al, Nature 464, 575-578 (2010)), to identify and understand the mechanisms that lead to specific lock-key pair binding. For lock pockets of a particular shape, we experimentally identify the importance of nonspecific lock-key binding as a pathway to specific lock-key pair formation. In this pathway, key particles can diffuse on the surface of the lock and bind specifically to the dimple of the lock. We find that this mechanism can be more important to specific bond formation than the direct binding mechanism. We model the surface diffusion mechanism as a mean first-passage time problem. Using an anisotropic interaction potential between a lock and key particle pair (van Anders et al, arXiv:1309.1187), we compare Stokesian dynamics simulations of lock and key binding to the experiments. We propose that nonspecific interactions can play an important role in accelerating anisotropic particle assembly. [Preview Abstract] |
Monday, March 3, 2014 10:48AM - 11:00AM |
A22.00015: Importing super-resolution imaging into nanoscale puzzles of materials dynamics John King, Chi Hang Boyce Tsang, William Wilson, Steve Granick A limitation of the exciting recent advances in sub-diffraction microscopy is that they focus on imaging rather than dynamical changes. We are engaged in extending this technique beyond the usual biological applications to address materials problems instead. To this end, we employ stimulated emission depletion (STED) microscopy, which relies on selectively turning off fluorescence emitters through stimulated emission, allowing only a small subset of emitters to be detected, such that the excitation spot size can be downsized to tens of nanometers. By coupling the STED excitation scheme to fluorescence correlation spectroscopy (FCS), diffusive processes are studied with nanoscale resolution. Here, we demonstrate the benefits of such experimental capabilities in a diverse range of complex systems, ranging from the diffusion of nano-objects in crowded 3D environments to the study of polymer diffusion on 2D surfaces. [Preview Abstract] |
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